Many methods are known in the art for providing fault tolerance and backup in communication networks. For example, U.S. Pat. No. 6,775,278, whose disclosure is incorporated herein by reference, describes a method for ensuring that a single and consistent reply is made to an address resolution protocol (ARP) request in a system of connected IP networks. When an adapter denoted A becomes active, the owning host sends an ARP advertisement into the network over the adapter. If the advertisement is also received at the sending host over a different adapter denoted B, the host knows that adapter B is on in the same physical network as adapter A. Adapter B can be designated as a backup adapter for A and A can be designated as a backup adapter for B.
If adapter A fails or becomes inactive, the host resets the backup adapter field for any adapter it owns for which A is marked as the backup adapter. If a backup adapter B has been designated for A, the host also sends an ARP advertisement associating the medium access control (MAC) address of adapter B (MAC-B) with the Internet Protocol (IP) address of adapter A (IP-A). This method allows network connections originally served via adapter A to continue to operate non-disruptively over adapter B, and also provides access to the host for subsequent new connections.
As another example, U.S. Pat. No. 6,760,859, whose disclosure is incorporated herein by reference, describes a method, program product, and apparatus for providing a non-disruptive takeover by a backup adapter when an adapter from a group of adapters connecting a data processing system to a local area network (LAN) fails. The adapters are arranged in one or more groups, with each group having at least two members, one member being a backup adapter in the idle state. Primitives, in accordance with the IEEE 802.2 standard, are monitored for each adapter. When a failure is detected, the medium access control (MAC) address for the failed adapter is loaded to the backup adapter, and the backup adapter is placed in the active state to non-disruptively take over the failed adapter.